NVIDIA Mellanox MCX312B-XCBT ConnectX-3 Pro EN Adapter Card, Dual-Port SFP+, 10GbE: This is a dual-port 10 Gigabit Ethernet network interface card based on NVIDIA Mellanox ConnectX-3 Pro silicon. Two SFP+ cages on a single PCIe 3.0 x8 host interface. This is the Pro variant (B-stepping silicon); it is NOT the base ConnectX-3 MCX312A-XCBT, and not the single-port MCX311A or MCX312B-XCDT variants. This is an Ethernet-only NIC; it does NOT support InfiniBand. This is a refurbished unit tested by T.E.S IT-SOLUTIONS.
Engineering Context
The card uses one ConnectX-3 Pro ASIC and exposes two SFP+ cages, both backed by the same PCIe 3.0 x8 host interface (8GT/s per lane, ~63Gb/s aggregate). Both ports running at 10GbE (20Gb/s combined) sit well within the PCIe budget. SFP+ cages support DAC cables, 10GBASE-SR/LR optical transceivers, and 10GBASE-T copper SFP+ modules. Pro silicon adds RoCE v2 and VXLAN/NVGRE encapsulation/decapsulation offloads beyond the base MCX312A. SR-IOV supports up to 127 virtual functions across both ports. Standard stateless TCP offloads (TSO, LSO, GRO) are supported.
Deployment & Use Cases
Dual-homed 10GbE host uplinks for active-passive or LACP bonded server attach. Storage server NICs (Ceph, NFS, iSCSI, iSER) needing redundant paths. Virtualization hosts (VMware ESXi, KVM, Hyper-V) with two SR-IOV-capable ports. RoCE v2 RDMA between dual-port hosts. Top-of-rack server attach in dual-fabric data centers. Replacement for older Intel X520-DA2 / Broadcom 57810S dual-port cards.
Technical Specifications
OEM: NVIDIA Mellanox
Part Number (MPN): MCX312B-XCBT
Product Line: ConnectX-3 Pro EN
Ports: Dual-Port SFP+
Ethernet Speed: 10GbE per port
Protocol Mode: Ethernet only
Host Interface: PCIe 3.0 x8 (8GT/s)
Form Factor: PCIe (full and low-profile brackets supported)
RDMA: RoCE v1 and RoCE v2
Overlay Offloads: VXLAN, NVGRE encap/decap
Virtualization: SR-IOV (up to 127 VFs)
Condition: Refurbished — Tested by T.E.S IT-SOLUTIONS
Compatibility & Hard Constraints
Requires a PCIe 3.0 x8 (or wider) slot. PCIe 2.0 slots will work but bandwidth is halved (still sufficient for 2x10GbE). Compatible with most third-party 10GbE switches at standard SFP+ speeds; SFP+ DAC cables and SR/LR transceivers from Mellanox, Cisco-coded, Arista-coded, and generic vendors are typically interoperable. Driver support requires MLNX_OFED or upstream Linux mlx4 drivers; the ConnectX-3 generation is NOT supported by the newer mlx5 driver. Does NOT support 25GbE — the SFP+ cages are hard-limited to 10G. Does NOT support InfiniBand. Two-port LACP/bond requires switch-side configuration.
Why Choose T.E.S IT-SOLUTIONS
T.E.S IT-SOLUTIONS bench-tests every ConnectX-3 Pro EN dual-port card for 10GbE link training on both ports, RoCE loopback, and PCIe link width before shipment. Visit T.E.S IT-SOLUTIONS for warranty terms and global shipping. Standard handling time 1–3 business days.